What is "bending"?

There are many missing notes on a normal 10 hole diatonic harmonica. To get those missing notes, we have to bend certain notes. Bending is basically a technique used to change the pitch of a note so we can reach the missing notes.

For example, if you take the 4th hole of a C harmonica, the blow note is a "C", and the draw note is a "D". The C# is missing. To get this C#, we have to bend the 4 draw D note down to C#.

Bending notes is what gives the harmonica its distinctive bluesy sound.

How is it done? Bending is one of the more difficult harmonica techniques to learn. Bending is accomplished using the tongue, throat and mouth to vary the pressure on the harmonica reeds. It's difficult to describe how exactly it is done since everything happens inside the mouth.